1. Field of the Invention
The present invention relates to a self-pumping hydropneumatic spring strut with internal leveling. More particularly, the present invention relates to a spring strut having an actuator for elevating a motor vehicle to a variety of levels.
2. Description of the Related Art
German reference DE 198 18 116 C1 discloses self-pumping hydropneumatic spring struts with internal leveling having a piston pump that is driven by the suspension movements and pumps oil out of a low-pressure chamber into the working space connected to the high pressure chamber. Driven by this pump, the spring strut keeps the vehicle at a constant distance from the ground, depending on its state of loading. This is a mechanical subassembly, the basic level of which does not require any electrical or electronic control. However, it has been found in practice that rather than be at a constant distance from the ground at all times, certain applications require the vehicle body to be elevated at different levels.
The prior art also includes externally supplied leveling devices capable of moving the vehicle body to various heights and keeping it there resiliently, irrespective of the state of loading, through the use of hydraulics or compressed air. For example, a central level of the vehicle body could be used for local driving, while a lower level of the vehicle body might be advantageous for freeway driving for reasons of aerodynamics. A high level of the vehicle body relative to the ground might be advantageous in order to avoid contact between the body and the ground when driving off road.
Self-pumping leveling devices can manage only a single level. Externally supplied leveling devices are of very complex instruction. In particular, a pneumatic spring requires not only a correspondingly large amount of installation space but also a compressor, an air dryer and pressurized fluid lines extending throughout the vehicle. The situation is similar with hydropneumatic systems (spring cylinders) require the engine compartment accommodate pressurized fluid lines leading to the individual spring cylinders from an oil pump and oil reservoir.
Furthermore, displacement detection systems (height sensors) are required to allow different levels to be adopted. These are often difficult to accommodate in the vehicle since they have to be installed between the vehicle body and the axle of the running gear. If the vehicle is also supposed to compensate for skew loads, a sensor is required for each wheel, in which case the displacement signals have to be processed by a corresponding electronic system and a control circuit.
It is the object of the present invention to create a simple self-pumping hydropneumatic spring strut in which a leveling device with more than one level can be created by simple means.
To achieve this object, the present invention provides for the spring strut to be assigned an actuator which displaces the spring strut in the vertical direction.
Advantageously, the spring strut assumes a desired level by mechanical means, irrespective of the state of loading, without the need for an electrical or electronic control system. The additional actuator provided is then used to modify the basic level. Both the actuator and the spring strut operate independently of the state of loading of the vehicle.
According to an easy to produce embodiment of the present invention, the actuator is constructed as a separate component and is arranged between the spring strut and the body and running gear, respectively. Advantageously, a standard spring strut can be combined with an actuator constructed as a subassembly and can be installed in the vehicle as a complete assembly.
According to a further embodiment, a subassembly can be created by making the actuator an integral part of the spring strut.
Irrespective of whether the actuator is a separate component or integrated into the spring strut, another advantageous embodiment allows the actuator to be driven electrically, hydraulically or pneumatically.
A particularly advantageous embodiment provides for the actuator to have a self locking means. To this end, the actuator is made as a spindle drive, worm gear, or the like.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.